In this project the effects of simultaneous stimulation of the dopamine system and impairment of the olfactory system on the social behavior of male hamsters are being studied. It has been found that apomorphine, a putative activator of dopamine receptors, greatly inhibits copulatory behavior and increases aggressive behavior in sexually active male hamsters. Apomorphine also increases aggression in olfactory bulbectomized males, indicating that the drug acts independently of the normal olfactory sensory control of aggression in hamsters. The only animals failing to show a response to apomorphine were four males in which lesions of the sensory nerve supplying the accessory olfactory bulbs had temporarily eliminated mating behavior. Lithium chloride which, like apomorphine, causes gastrointestinal distress, had no effect on the mating behavior of hamsters.